JNK-Interacting Protein 3 Mediates the Retrograde Transport of Activated c-Jun N-Terminal Kinase and Lysosomes
(A) Induction of caJNK3-EGFP at 4 dpf increased the level of pJNK immunofluorescence (middle) in a subset of axon terminals but did not lead to lysosome accumulation as compared to control (B). Scale bars = 10 µm. (C, D) This result was confirmed by Lysotracker red labeling. Surrounding, non-caJNK3-EGFP positive axons show similar numbers, size and density of lysosomes both 4 hours and 13 hours after induction of caJNK3. The pLL nerve was visualized by phase contrast optics and is outlined. Arrowhead indicates axonal swellings caused by high levels of activated JNK. HC denotes neuromast hair cells that strongly label with Lysotracker red. (E) Whole embryo expression of Jip3 and Jip3ΔJNK by mRNA injection partially suppressed the accumulation of lysosomes in jip3nl7 mutant axon terminals at 3 dpf as assayed by expression of Lamp1-mTangerine in pLL neurons. Wildtype – Lamp1-mTangerine positive small puncta only; Mild – small puncta and aggregates visible; Severe - few to no small puncta apparent and large aggregations of Lamp1-mTangerine. (F–I) Injection of 10 pg of a DNA construct encoding Jip3ΔJNK-mCherry rescued lysosome accumulation in jip3nl7 axon terminals. Larvae that expressed Jip3ΔJNK-mCherry (red) in pLL axons and carried the neurod:EGFP transgene were first imaged live (F,H) to identify expressing axon terminals. They were then individually fixed, stained for pJNK (pseudo-colored magenta) and Lamp1 (white), and subsequently the same axon terminals were reimaged (G,I). Arrowheads point to axon terminals in wildtype (F,G; NM1) and jip3nl7 (H,I; NM5) that express Jip3ΔJNK-mCherry (red) at 5 dpf. Arrows point to axon terminals in the same NMs that did not express this construct. Note that expression of Jip3ΔJNK-mCherry in jip3nl7 completely rescued lysosome accumulation (yellow arrowheads in I″) but failed to rescue high levels of pJNK (yellow arrowheads in I′).